The overall objective of this study is to apply genetic principles as a tool in assessing the mechanisms of intestinal epithelial cell and erythrocyte transport of amino acids. Goals for the current year include breeding studies to continue the development of high and low absorbing lines for leucine transport in the erythrocyte. Line separation will be analyzed by growth trials, kinetic studies, developmental studies, analysis of transport of substrates which employ separate carriers, comparison of transport in erythrocytes with that in the bowel, analysis of ATPase and cellular alkali ion concentration.